<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    var obj = {};
    Object.defineProperty(obj,"age",{
        writable:true,
        value:18,
    })

    console.log(obj)
</script>
</html>